Methods of culturing microorganisms or cultured cells and continuously collecting products are known. Specifically, a method of continuous fermentation is developed that separates a product from a microorganism or the like using a filtration membrane and returns the microorganism or the like contained in an unfiltrated liquid to a culture liquid again.
In the method of continuous fermentation, a sterilized culture medium is continuously supplied to culture a microorganism or cultured cell continuously. To continuously supply the sterilized culture medium, the method of continuous fermentation uses a continuous sterilizing apparatus that can continuously sterilize the culture medium. The continuous sterilizing apparatus can sterilize the culture medium by short-time heating treatment.
To industrially produce fermented products at low prices, in general, a large volume of products are desired to be produced at a time. In this case, a fermenter of a fermenting apparatus for use in continuous fermentation treatment has a scale of several hundreds of tons. When sterilization treatment is performed on a culture medium housed in a fermenter of this scale, it requires long time to heat the culture medium at the center of the fermenter to a temperature appropriate for sterilization, and the culture medium may deteriorate through long hours of heating. Given these circumstances, batch sterilization that performs sterilization practically for each fermenter is not performed as culture medium sterilization treatment. For this reason, a continuous sterilizing apparatus that can perform high-temperature, short-time sterilization and can minimize deterioration of a culture medium through heating is suitably used in culture medium sterilization treatment.
The continuous sterilizing apparatus includes a heating unit that heats a liquid to be sterilized, a holding unit that holds the temperature of the heated liquid to be sterilized for a set time to perform sterilization, and a cooling unit that can cool the sterilized liquid to be sterilized nearly to room temperature (refer to Japanese Laid-open Patent Publication No. 2000-262594, for example).
The continuous sterilizing apparatus includes, as a form of heating the liquid to be sterilized, a multi-pipe type, a plate type, and a steam injector type. The steam injector type is a type of directly introducing steam into the liquid to be sterilized, can instantaneously increase the temperature of the liquid to be sterilized, and can simultaneously sterilize the inside of the continuous sterilizing apparatus (refer to Japanese Laid-open Patent Publication No. 01-148180, for example). However, a boiler compound (an anticorrosive) usually mixes with steam used in industrial processes, and the boiler compound mixing with a culture medium may affect fermenting performance. For this reason, in fermenting processes such as a method of continuous fermentation, the multi-pipe type or plate type is used. Although the multi-pipe type and plate type can perform continuous sterilization treatment without using the boiler compound, heating treatment enough for instantaneously increasing the temperature of the liquid to be sterilized cannot be performed, unlike the steam injector type.
FIG. 10 is a schematic diagram illustrating an example of a rough configuration of a conventional multi-pipe type continuous sterilizing apparatus. The continuous sterilizing apparatus 100 illustrated in FIG. 10 includes a pressure feed pump 101 that pressure feeds a culture medium, a food product, or a pharmaceutical (hereinafter, referred to as a liquid to be sterilized) to be pressure-fed and a sterilizing liquid, a heating unit 102 that heats the liquid to be sterilized or the sterilizing liquid sent by the pressure feed pump 101, a holding unit 103 that holds the liquid to be sterilized or the sterilizing liquid heated by the heating unit 102 at a certain temperature for a certain time, a cooling unit 104 that cools the liquid to be sterilized or the sterilizing liquid held by the holding unit 103 and for which heating sterilization has been completed, and a cooling unit 105 provided at the rear of the cooling unit 104 and cools the sterilizing liquid, which are connected to each other with pipes to form a flow channel. Operation of the continuous sterilizing apparatus 100 is controlled by a controller (not illustrated).
In the continuous sterilizing apparatus 100, the pressure feed pump 101, the heating unit 102, the holding unit 103, and the cooling unit 104 are connected in order with a pipe 106 to form a first flow channel as a flow channel. In addition, in the continuous sterilizing apparatus 100, a second flow channel is formed by connecting an upstream side end and a downstream side end of the pipe 106 and both ends of a pipe 107. The cooling unit 105 is provided in the second flow channel.
The pipe 106 includes a valve 111 provided at the front of the pressure feed pump 101 and valves 112 and 113 provided at the rear of the cooling unit 104. The valve 112 is provided at the front (upstream side) of a connecting part between the pipe 106 and the pipe 107, whereas the valve 113 is provided at the rear (downstream side) of the connecting part between the pipe 106 and the pipe 107. The pipe 107 includes valves 114 and 115 provided near the respective connecting parts with the pipe 106. The valve 114 is provided at a connecting part with the downstream side of the first flow channel (the pipe 106) in the pipe 107. The valve 115 is provided at a connecting part with the upstream side of the first flow channel in the pipe 107.
The heating unit 102 circulates steam through the inside of a pipe 102a provided along the pipe 106, thereby heating the pipe 106. The cooling units 104 and 105 circulate cooling water through the inside of pipes 104a and 105a provided along the pipes 106 and 107, respectively, thereby cooling the pipes 106 and 107, respectively.
The continuous sterilizing apparatus 100 circulates the sterilizing liquid through the inside of the pipes 106 and 107 to perform sterilization treatment on the inside of the pipes as pretreatment of continuous sterilization treatment before circulating the actual liquid to be sterilized. Specifically, with the valves 112, 114, and 115 open and with the valves 111 and 113 closed, the sterilizing liquid is circulated through the inside of the pipes 106 and 107 by the pressure feed pump 101, thereby sterilizing the inside of the pipes 106 and 107. In that situation, the sterilizing liquid circulates through the pipes heated up to about 135° C. by the heating unit 102 and is cooled to about 50° C. by the cooling unit 105. The continuous sterilizing apparatus 100 adjusts the operation of the pressure feed pump 101 and an open state of the valve 112 by the controller, thereby controlling a flow rate and pressure within the pipes. During the sterilization treatment, the cooling unit 104 stops its cooling operation. With this operation, the sterilizing liquid circulates through the pipe 106 heated up to about 135° C. to sterilize the inside of the pipe, is cooled by the cooling unit 105, and again flows into the heating unit 102.
After the sterilization treatment with the sterilizing liquid, the cooling unit 104 is operated to stabilize a cooling temperature inside the pipe 106 in the cooling unit 104. Control to open the valve 113 and to close the valves 114 and 115 is then performed, the valve 111 is opened to switch from the sterilizing liquid to the liquid to be sterilized, and the continuous sterilization treatment on the liquid to be sterilized is performed.
In the conventional continuous sterilizing apparatus 100, the cooling unit 105 is provided in the second flow channel used for the pretreatment, in addition to the first flow channel as the original sterilizing channel, and the apparatus is disadvantageously large in scale.
It could therefore be helpful to provide a method of operating a continuous sterilizing apparatus, a continuous sterilizing apparatus, a fermenting system, and a continuous fermenting system that can surely perform sterilization treatment on the inside of a flow channel and achieve downsizing of the apparatus.